THE ACTION OF SULPHURIC ACID ON GLIADIN: WITH SPECIAL REFERENCE TO THE N-PEPTIDYL→O-PEPTIDYL BOND REARRANGEMENT

Abstract

Treatment of gliadin with sulphuric acid transposes peptide bonds of serine from the amino to the hydroxyl group. Maximum transposition, 60–70% of the theoretical, occurs when the protein is treated with anhydrous sulphuric acid at 0°C. for 35 hr. No rearrangement was detected at threonine residues. Examination of the peptide material, obtained from the rearranged protein by Elliott's degradation method, indicates apparent "homogeneity". In an alternative scheme for the degradation, nitrous acid deamination of free amino groups was used. The resulting loss in serine content of the protein is direct evidence for the acyl migration of peptide bonds. Incorporation of sulphur and partial disappearance of several amino acids accompany the sulphuric acid treatment. The occurrence of these secondary reactions imposes limitations on the use of sulphuric acid as a reagent for the specific fission of peptide bonds.